1. Field of the Invention
The present invention relates to synchronous Ethernet, and more particularly to an asynchronous data segmentation/transmission method for synchronous Ethernet and a data structure used therein.
2. Description of the Related Art
Generally, Ethernet is one of the common technologies for communicating data between a variety of terminals through a LAN (Local Area Network). However, the Ethernet technique is not suitable for transmission of moving pictures or voice data that are sensitive to transmission time delay. A technique for synchronously transmitting data such as image and voice has been actively researched and developed based on the conventional Ethernet. This technique is called synchronous Ethernet.
FIG. 1 is a view illustrating a transmission frame structure for general synchronous Ethernet.
As shown in FIG. 1, the transmission frame based on one transmission cycle includes an asynchronous (hereinafter referred to as Asynch) frame part 11 for asynchronous data transmission, a control frame part 12 for control frame transmission, and a synchronous (hereinafter referred to as Sync) frame part 13 for synchronous data transmission. The transmission frame has a transmission cycle of 125 μs.
More specifically, the Synch frame part 13 for synchronous data transmission has the highest priority in the transmission cycle. According to a currently proposed standard (which my be changed in the future), the Synch frame part 13 includes a plurality of 738-byte sub-synchronous frames, basically 10.
Also, the control frame part 12 for control frame transmission includes a TSC (Time Sensitive Control) frame for time control and an MDCP (Media Device Control Protocol) frame for controlling media devices.
Further, the Asynch frame part 11 for asynchronous data transmission includes variable synchronous data based on frame units.
FIG. 2 is a diagram illustrating the structure of general asynchronous data.
As shown in FIG. 2, general asynchronous data, such as Ethernet data, is composed of 7 bytes. The general asynchronous data includes a Preamble field 301 for indicating a start and end of a frame, an SFD (Start-of-Frame Delimiter) field 302, composed of 1 byte, for identifying a byte unit in a frame bit sequence and indicating a start of contents of the frame in a normal state, a Destination Address (DA) field 303, composed of 6 bytes, for indicating a destination MAC (Media Access Control) address to be transmitted to the transmission frame, a Source Address (SA) 304, composed of 6 bytes, field for indicating MAC address of a station transmitting the frame, a length/type (L/T) field 305, composed of 2 bytes, for indicating length information of data in the transmission frame and type information of protocol for the transmission frame, a data field 306 for indicating data of the frame, and a FCS (Frame Check Sequence) field 307, composed of 4 bytes, for detecting errors at respective ends of frames into which information is segmented for transmission.
Frequently, the Preamble field 301 and the SFD field 302 may be represented by a Preamble field including the SFD field 302. In that case, the Preamble field may be composed of, for example, 8 bytes.
FIG. 3 is a diagram describing general asynchronous data transmission in synchronous Ethernet, in which there are two transmission frames based on two transmission cycles.
As shown in FIG. 3, a first transmission frame based on a first transmission cycle includes a Synch frame part 13-1, a control frame part 12-1 and an Asynch frame part 11-1. A second transmission frame based on a second transmission cycle includes a Synch frame part 13-2, a control frame part 12-2 and an Asynch frame part 11-2.
Since the Synch frame parts 13-1 and 13-2 and the control frame parts 12-1 and 12-2 are not related to the subject matter of the present invention, a detailed description thereon will be omitted. Instead the Asynch frame parts 11-1 and 11-2 will be described in detail as below.
The Asynch frame part 11-1 includes Asynch frames 201, 202 and 203, which are variable in length. The Asynch frame part 11-2 also includes Asynch frames 204, 205 and 206, which are variable in length. Accordingly, since the respective Asynch frames are variable in length, their sizes are also different.
In order to perform operations of the transmission frames, if the length of the last Asynch frame 203 within the first transmission cycle 11-1 is L1 and Asynch data 21 to be transmitted has a length of L2, the two lengths are compared before the Asynch data 21 is inserted into the transmission frame for the transmission cycle. If L1 is equal to or greater than L2, the Asynch data 21 to be transmitted is inserted into the Asynch frame 203 and then transmitted to a predetermined destination.
If L1 is less than L2, the Asynch data 21 to be transmitted cannot be inserted into the Asynch frame 203. Therefore, the Asynch frame 203 without data is transmitted to a predetermined destination. Instead the Asynch data 21 is inserted into the first Asynch frame 204 within the second transmission cycle 11-2 and then transmitted to a predetermined destination.
As such, in the prior art transmission method, the Synch frame part and control frame part within a transmission cycle of 125 μm are first transmitted to a predetermined destination and then the Asynch frame part is transmitted based on the comparison of the last Asynch frame length with the length of the Asynch data to be transmitted. However, if the length L2 of the Asynch data 21 is not equal to the length of the last Asynch frame, the Asynch data 21 is not transmitted during the first transmission cycle, and instead must be inserted into the next transmission frame for the next transmission cycle.
Therefore, the prior art transmission method has a disadvantage in that, since a transmission frame including an Asynch frame without Asynch data to be transmitted is transmitted based on a first transmission cycle if the sizes of the Asynch frame and the Asynch data are different from each other, it wastes bandwidth corresponding to the size of the Asynch frame during the first transmission cycle.